The present invention generally relates to electrophotography, and more particularly, to an electrophotographic process and an apparatus employed therefor which may be applied to a printer, facsimile device or the like.
Conventionally, in the field of electrophotographic developing method, there have been proposed the cascade developing process, touch-down developing process, and jumping developing method, etc., among which the cascade developing process disclosed, for example, in the U.S. Pat. No. 3,105,770 is known as a developing process in which a developing material is directly sprinkled over a photosensitive member or photoreceptor. Such a cascade developing method is the developing process applied to a first copying apparatus for a practical application based on the electrophotographic method.
Moreover, there is another developing process in which the developing is effected by causing a mono-component toner to fly, through impression of A.C. bias onto a developing roller as disclosed for example, in U.S. Pat. No. 3,866,574, in which it is stated that the A.C. bias to be applied to the developing roller is used for the purpose of activating the movement of toner, and the toner reaches the image portion by flying, while some of the toner is returned in the course of flying back to the non-image portion.
Furthermore, as a developing method in which the technique for applying such A.C. bias has been improved, there has been proposed a jumping developing method as disclosed in Japanese Patent Publication Tokkosho No. 63-42256, which is so arranged that the toner supported by a toner supporting member is carried up to a developing section, where the toner is caused to adhere to an image portion of a photosensitive member by an A.C. bias. The technical concept in this Japanese Patent Publication Tokkosho No. 63-42256 is different from that of the above U.S. Pat. No. 3,866,574 in that the toner is subjected to reciprocating movement at the image portion and the non-image portion.
As is well known in this field of technique, the cascade developing process is weak in the reproduction of solid images, with a further problem that an apparatus therefor tends to be large and complicated. Moreover, the developing apparatus of the U.S. Pat. No. 3,866,574 has such disadvantages that a high accuracy is required for the apparatus, with complicated constructions, and a consequent high cost. In the jumping developing process, since the photosensitive member is developed by the toner support member supporting the toner layer, it has been indispensable that an extremely uniform thin layer is formed on the toner supporting member in order to obtain a high quality image. Additionally, in the above process, the so-called "sleeve ghost" phenomena took place in which hysteresis of a former image often remains on the toner thin layer of the toner support member, thus appearing as an after-image in the resultant image, with further disadvantages that the apparatus therefor is complicated in construction, thus resulting in high cost.